We thought she'd outgrown and tried a rear basket. The problem there is you can't see what the dog's up to and they can't see where they're going, which makes it unhappy for both of you. Also that particular basket isn't high or square enough.
I wouldn't worry too much about them jumping out, at least once they've got used to it. Start them early!
Here's our 8-9 kg spaniel in a bog standard cheapo front basket with no additional support. Works fine, but she's been using it since she was a puppy. A setup like Midi's would be ideal for a slightly bigger dog.
We thought she'd outgrown and tried a rear basket. The problem there is you can't see what the dog's up to and they can't see where they're going, which makes it unhappy for both of you. Also that particular basket isn't high or square enough.
I wouldn't worry too much about them jumping out, at least once they've got used to it. Start them early!